Foxing is a term describing the age-related spots and browning seen on vintage paper documents such as books, postage stamps, certificates, and so forth. The name is believed to derive from the fox-like reddish-brown color of the stains. Paper so affected is said to be "foxed."

While unsightly, and a negative factor in the value of the paper item for collectors, foxing does not affect the integrity of the paper.

Foxing also occurs in biological study skins or specimens, as an effect of chemical reactions or mould on melanin.

Causes of Foxing

The causes of foxing are not well understood. One theory is that foxing is caused by a fungal growth on the paper. Another theory is that foxing is caused by the effect on certain papers of the oxidation of iron, copper, or other substances in the pulp or rag from which the paper was made. It is possible that multiple factors are involved.

It is believed that high humidity contributes to foxing.

Repairing foxed documents

There are products available which were specifically designed to remove foxing. The problem with using proprietary bleaches to remove foxing is that they invariably affect the integrity of the paper and the paper has to be subsequently resized.

Using laser-based techniques to remove foxing stains from old paper is a potential solution to the problem. The use of lasers however, at longer wavelengths, is usually accompanied by side effects, since the affected area requires higher laser energies to be cleaned.

Depending on how valuable one's print or map is, one could try lightly dabbing 3% hydrogen peroxide onto the affected area using a cotton swab or cotton bud. This process is effective but one should test the paper in a less critical area first. It doesn't take much and one should not soak the spots; the hydrogen peroxide will bleach the ink just as it will bleach the foxing. Patience and repeated applications are best.

Foxing in biological specimens

It is generally not advisable to repair study specimens, except maybe for mechanical damage. Type specimens should, if by any means possible, not be altered in any way. If foxing affects the study value of a specimen (e.g. in bird or mammal skins or in insects, where it might affect diagnostic coloration), this might rather be remarked on the specimen label. Color standards can provide a means of documenting coloration before or in the early stages of foxing.

References

• Smithe, Frank B (1974): Naturalists' Color Guide Supplement. American Museum of Natural History, NYC. ISBN 0-913424-04-8
• Smithe, Frank B (1975): Naturalist's Color Guide (2nd ed.). American Museum of Natural History, NYC. ISBN 0-913424-03-X
• Smithe, Frank B (1981): Naturalist's Color Guide Part III. American Museum of Natural History, NYC. ISBN 0-913424-05-6
• Roberts and Etherington, Bookbinding and the Conservation of Books
• Antique Roadshow: 'Antiques Speak'
• The Library of Congress: 'Preserving Works on Paper'